Manufacture of fluoroorganic compounds



Patented May 5, 1953 UNITED STATES .A'ELENT' OFFICE MANUFACTURE OF FLUORODRGANIG. COMPOUNDS NoDrawing. Application October 2, 1951, SerialNo. 249,403

(Cl. 260-653.)v

7 Claims. 1

This invention relates to preparation of fluorine-rich organic compounds useful in the refrigerating and propellant fields and as chemical intermediates. The present improvements are directed to. processes for manufacture, by disproportionation methods, of aliphatic fluorocompounds rich in fluorine from aliphatic fiuorocompound starting materials to lower the fluorinecontent.

The. starting materials of the invention comprise. fiuoroderivatives of methane which contain not more than one fluorine atom and at least two halogen, e. g. chlorine, atoms other than fluorine, and which may or may not contain a hydrogen atom Specifically, suitable starting materials are CClaF and CHClzF.

Several processes are known for fluorine-ting organic compounds. Thus, it. has been proposed to employ fluorine, hydrogen fluoride, or metallic fluorides such as mercuric fluoride and antimony t'rifiuori'de as fiuorinating agents with or with out catalysts. It has also been developed that aluminum fluorides of extremely small crystal size, hereinafter more fully described, have the property of catalyzing disproportionation of the starting materials of the invention to form more highly fiuorinated methane derivatives containving. two or more fluorine atoms, e. g. products such. as CClzFz and CClFs.

' In connectionwith production by various commercial methods of certain halofluorocarbons such as CClzFz, substantial amounts of CClsF are formed as a lay-product- In some: instances it is desirable to convert such CClsF to the more highly fluorinated. and. presently more valuable CClzFz, and the above mentioned aluminum fluoride method for disproportionating C0135 issat isfactory for this purpose. However, there are also circumstances: in which it is desirable to convert CClsF to CClzFz under temperature conditions which may vary over relatively wide tem-- perature ranges, and at the. same time produce maximum quantities of CCIzFz. andv minimum quanties of more highly fluorinated material such as CClFs, i. e. to proceed in such a way as to minimize or inhibit formation of fiuoroderivatives' of methanecontai'ning more than two fluo-- rine atoms.

The principal object oi the invention is to provide for manufacture. of fiuoroclerivatives of methane containing not. more than two iiuori-ne atoms from the starting materials indicated by processes which minimize or inhibit formation of fiuoroderivatives of. methane containing more than two fluorine atoms and which do not. re-

quire the use of. fiuorinating agents which are expensive, difficult to make, and troublesome to use: and handle. Another object is provisionof completely gas phasemethods for preparing twofluorine-atom derivatives of methane from the starting materials: noted by means of easily controlled disproportionation operations made possible by conjunctive use of the particular hereindescribed aluminum fluoride catalysts and a-certa-in inhibiting agent;

Procedure of the invention includes contacting agaseous materia1 comprising a fluoroderiva-tive of methanev containing not more than one fluorine atom and at least two halogen atoms other than fluorine, at elevated temperature, with the hereindiescribed aluminum fluoride catalysts. In accordance with the invention, it has been found that when. the foregoing contacting operation is carried out: in the presence of a small amount of nitric oxide (NO) disproportionation of the starting material to compounds containing more than two fluorine atoms is minimized or inhibited. Hence, general practice of the invention includes contacting a fluoroderivative of methane containing not. more than one fluorine atom and at least two halogen atoms other than fluorine, at disproportionation temperature not above about 40.0 C.,. with the hereindescribed aluminum fluoride catalysts. While maintaining. in the. reaction zone the presence of NO in amount sufficient to decrease formation ofv compounds containing more than. two fluorine atoms.

The majority of aluminum. fluorides known in the art consist of lumps or smaller discrete particles which in turn are composed of AlFa crystals ofv relatively large size, i. e. not less than one thousand. and usually several thousand Angstrom units radius and above as in the caseof commercial types of aluminum fluoride available on the market. However, certain forms of AlFz, when examined even by the highest powered optical microscope, appear to be of non-crystalline or amorphous structure. When such amorphous aluminum fluorides are examined using X-ray diffraction. technique, extremely small,

sub-microscope crystals, crystallites, may be detected, In practice of this invention, such amorphous. substantially anhydrous aluminum fluorides, having crystals of certain sub-microscopic (crystallite) size, are used in the disproportionate operations outlined above. Enhanced catalytic activity may be noted by use of aluminum fluorides of crystallite size of about 500 Angstrom radius or below and accordingly the advantages of the invention may be realized opwithin the scope of the invention regardless of method of preparation, However, according to a particular embodiment of the invention, improved catalytic material is employed which is prepared by treating aluminum halide other than,

aluminum fluoride (which halide is preferably in pure form but may suitably be of commercial or technical grades) with preferably excess quantities of inorganic fluorinating agent reactive therewith under conditions such that no liquid water is present in the reacting materials. For example catalyst may be prepared by treating solid hydrated aluminum halide with gaseous fluorinating agent (said agent being preferably, but not necessarily, anhydrous) at temperature high enough so that the water in the hydrate is volatilized into the gas, e. g. preferably above about 100 C. to 1 C.. the maximum temperature for avoiding fusion depending largely upon the degree of hydration of the reactant and the water content, if any, of the fluorinating agent. If desired, anhydrous reagents may be employed, in which case maintenance of particular temperatures during the catalyst preparation reaction is not as critical and said reaction may be carried out with fluorinating agent in the liquid phase. Of the fiuorinatin agents which may be used for catalyst preparation, boron trifiuoride and hydrofluoric acid may be mentioned. Anhydrous hydrofluoric acid is preferred. Anhydrous aluminum chloride is the preferred halide. Catalyst synthesis reaction is believed to proceed as follows:

HF displaces HCl causing transformation of A1013 into AlFs. may be activated by heating in an anhydrous atmosphere at elevated temperature, 1. e. temperature at which activation takes place (presumably accompanied by vaporization and removal of any amounts of water of hydration). The finished catalyst is then recovered. Heating the AlFs in a stream of dry nitrogen or HF gas for about one to four hours at temperatures of about 300-350 C. or four to six hours at 250- 300 C. is ordinarily suitable for this purpose. If desired, the catalyst may be activated by heating the AlFs in a stream of free oxygen-containing gas such as oxygen or air at about 100-600 C. for approximately minutes to eight and onehalf hours (depending mostly on the 02 content of the treatment gas), in which case activation with dry nitrogen or HF gas as aforesaid. may be omitted.

Although not essential to realization of the objects of the invention, a suitable and convenient procedure fOr preparing the aluminum fluoride catalyst is to add solid anhydrous aluminum chloride to an excess of liquefied anhydrous hydrofluoric acid in a cooled container and, after complete addition of the aluminum chloride, F

mildly to agitate the mixture until reaction is substantially complete. The AlF; so prepared may be then activated as outlined above. Following is Example A illustrating preparation of A1F3 catalyst according to the latter procedure.

The remaining aluminum fluoride Example A 300 parts by weight of granular (8 to 18 mesh) anhydrous aluminum chloride of commercial grade were added in small portions to liquid anhydrous hydrofiuoric acid contained in an externally cooled vessel. A vigorous exothermic reaction took place and additional amounts of hydrofluoric acid were added as needed to maintain an excess thereof. After all the aluminum chloride had been added, the mixture was stirred to promote residual reaction. When reaction of aluminum chloride appeared complete, the mass wa mixed and stirred with additional liquid hydrofluoric acid and excess HF was removed by slowly boiling the mixture. 200 parts of anhydrous aluminum fluoride of about 10-40 mesh size having greater than 98% AlFz content and containing less than 0.15% chlorine were recovered. This AlFs Was heated in a stream of dry inert gas (nitrogen) at a sufiiciently elevated temperature (250-300 C.) and a period of time sufiiciently long (4-6 hours) to drive off residual amounts of water and activate the material. An X-ray difiraction pattern of material prepared according to the method outlined above, indicated crystallite size to be less than 100 Angstrom units radius, i. e. the crystallite size was so small as to be indicative of amorphous structure as desired for the purpose of the present invention. The mesh size distribution of the AIR; particles did not change appreciably during the latter heat treatment.

As indicated above a particular procedure utilizing HF gas a fluorinating agent for the A1013 comprises treating anhydrous AlCb or the hydrate with HF gas (preferably anhydrous) at temperature sufficiently high to cause reaction between A1013 and HF and to volatilize and main,- tain any water present in the system in the gas phase (preferably 100-170 C., consistent with avoidance of fusion, in case the hydrate is employed), but low enough to prevent excessive volatilization of AlCls (preferably below about C. when anhydrous A1013 is treated), and thereafter activating the AIR"; produced. Aluminum fluoride so prepared has also been found to be composed of crystallites of size substantially below 200 Angstrom. Gas phase preparation of catalyst is illustrated by the following example, in which parts expressed are by weight.

Example B 600 parts of 4 to 18 mesh anhydrous aluminum chloride of commercial grade were charged to a nickel reactor and heated therein while passing through the reactor a stream of anhydrous HF gas to bring about the following reaction:

The HF was admitted at a sufliciently slow rate to keep the temperature in the reaction zone (exothermic reaction) below about 90 C. to prevent excessive loss of AlCls by volatilization. As the reaction neared completion, as evidenced by a sharp decline in reactor temperature, heat was applied externally to the reactor and temperature raised to about 300 C. while still continuing passage of a slow stream of HF through the tube, until last traces of AlCl; were converted to AlFs. The AlF3 so formed in this particular instance was then activated by heating it in a stream of air at about 450-500" C. for about 30 minutes. The size and shape of the solid material was about the same before and after treatment with gaseous HF. 500 parts of anhydrous aluminum assures fluoride W599i}. and; less; 01.15% chlorine, were recoveredan .X -ray fraction pattern either-material. prepared accord-j.

ing to the latter gas: phaseiprocednre made which .mdic'ated crys tallite size to be in therange 1430 2610 Angstromunits average being 140 IL, i. e. the crystallite size was so small as to T be indicative of amorphous structure as "desired for nuorination of unsaturated hydrocarbon If desired, the-catalyst maybeused in the-form of a fluidized solid bed. or suspended on a nonsiliceous inertcarr-ier such as activated alumina, Suitable methods: for

derivatives according to present invention.

metal fluorides or nickel, preparing this suspended catalyst include dis-jsolving the aluminum compound a solvent therefor, applying the solution to the: carrier, evaporatingthesolvent then treating the aluminum compound carrier fiuorinating agent; According. to an alternative" procedure, thealuminum compound, if volatile. may be: heated and thereby sublimed into a" as stream. and'subsequently condensed" onthe carrier.

after which. it-is treated: with fluorin-ating: agent as above. H be dissolved in ethyl chloride or an aqueous sole vent, then applied to the carrier, and subse-l I quently treated with hydrofluoric acid, or. aluminum chloride may be volatilized. into a gas stream condensed on the carrier, and" then treated to 5 convert it to aluminum fluoride. Practice of" the invention involves contacting a gaseous material comprising. a compound oft'lie group consisting of" @6135" and @HCIZF; at disproportionation temperature not above 400 (3., with the. above described aluminum fluoride cata lysts, having crystallite size below about 50o Angstrom units. radius, preferably not substantially greater than and? usually below about 200 Angstrom units radius, while in the presence of NO in amount sufficient to decrease, minimize or inhibit formation of products containing more than two fluorine: atoms such as CClFaand-CHFa. It has been found that the inhibiting properties of NO are not dependent upon temperature. Hence, temperature may vary widely; and: it: has been found that satisfactory temperatures may lie in the range of '75-4'=00 preferred tempera? tures lying in the range of 150-350 C. The con densation of liquid material on catalyst has a noted deleterious effect. upon its activity and, accordingly, temperatures'in all instances should be maintained above the temperature at which" any material tends to condense out on the catalyst. at the. pressureloi? thesystem'. Pressures may be reduced. or elevated; but pressures approxi mating atmospheric and; sutfi'cient to move: the

gas. through; the: system are: satisfactory According to apreferredphase or? the: invoicethen, the initialstarting material is CChF. As abovenoted with respect to production OfC'GleFz by certain. commercial methods, substanl'iia lv Specifically, aluminum chloride may. g

' 6 amour; and a very low ratio of CClFa to CCl'zE'r.

indicated, the inhibiting agent of. theinvention 1's. nitric oxide: (N0 ).v This gas may be metered into the reaction zone, along with the organicv compound starting material, by any suitable; means. Quantities of. .NO' employed may vary from any" small amount, suflicient to signifi- 'cantly reduce the amount of threeefluorine-atom compound which would otherwise be produced, up to a total of. not substantially in excess of 5% by weight of the organic compoundstarting material. The: NO- is? preferably used in the substantially pure form in amounts in the range of 1-5% by weight of the organic compound input. The NO maybe supplied to the process in the form of methyl or ethyl nitrite,ior nitro ethane, or any similar' material which: at the temperature of the reaction breaks down to yield N0 and which does not adversely afiiect the reaction or create reaction zonerexit gasj handling problems.

There is no critical maximum. time of contact of the organic reactant withaluminum fluoride catalyst and. the inhibiting agent. At long con-- tacttimes, however, the capacity of the reactor is low, and. an economic disadvantage inh'eresin the operation. 0n the other hand, if time of contact? is too short the reaction or organic compound: input toproduce the desired product may be incomplete; Thisresults in the appearance of relatively small amounts oi sought-for material and relatively large amounts of unreacted 'CClsF' the: reaction product. Such unreacted CClrF may be recovered from the product and returned to'the reaction, but in such operation cost of. recovering and' recycling unreacted material may amount to an appreciable item Accordingly, the time of contact employed is determined by balancing the economic. advantage of high reactor capacity obtained at short contact times against. cost of recovery of unreacted organic compound input. Further; flow of gaseous reactants through the reaction zone is dependent upon; variables such as.- scale of. the operation, quantity of catalyst in. the reactor, and specific apparatus employed, andioptimumz rate of flow of reactant and inhibiting agent, and optimum proportion of NO for any given conditions may be determined by a test run.

For convenience, atmospheric pressure operation is preferred,,but the reaction may, if desired, be carried out at superatmospheric or subatmospheric. pressure.

The process or. the invention may be suitably carried out by introducing a gas comprising e. g. CC13F and the. desired quantityof inhibiting agent into a reaction zone containing aluminum fluoride: described above and heating said materialinthe zone atthe: temperatures heretoiore indicated for. a timesufficient to convert an appreciable amount of CClsF to a compound richor in fluorina, withdrawing gaseous products from the zone and recovering said compound richer. infiuorinefrcm the gaseous products. Al'- thoughnot limitedto continuous operations, the

" process of my invention may be advantageously carried out. thereby.v

The. various reaction products may be recovcred. separately or in admixture from the reaction zone? exit gas stream in any suitable manner. The gas: discharged from the reactor zone is cooledin 32.00111181'1861 to: about 30: C. to con-- dense CCL; (B. P. 78 C.) and thence passed to a concentrated; H2604. scrubber to remove. NO, to a soda-lime tower toremove from the gas stream possible'traoesof HRHCL and. 012,. to a CaClz tower to remove any possible traces-ofwater, and to a vessel externally cooled with Dry Ice and acetone to condense CClzFz (B. P. minus 29.8 0.), some CClFb (B. P. minus 81 C.) and any unreacted CClsF (B. P. 23.8 C.). In event that appreciable amounts of CClFa are present in the product, the off-gas from the Dry Ice-acetone cooled condenser may be passed subsequently through a condenser cooled by, e. g." liquid nitrogen to a temperature of about minus 200 C. to condense any CClFs. Individual compounds may be recovered, e. g. by distillation, from the condensates obtained as above. Unreacted CClsF recovered may be recycled to subsequent operation.

In the case of use of CHClzF as starting material, the reaction product gas may be cooled to prelim narily condense out CHCls (B. P. 61.2 C.), scrubbed with H2804, soda-lime and CaClz, and then passed into a Dry Ice-acetone cooler to condense CHClFz (B. P. minus 408 C.). If appreciable amounts of CHI-3 (B. P. minus 822 C.) are present, the gas stream may be run through a liquid nitrogen cooler to condense this material.

The exact mechanisms of the disproportionation of the organic compound input taking place in the practice of the invention are not wholly understood, and the action of the inhibiting agent is not known. It is believed that the alu- "minum fluoride acts essentially as a catalyst at the temperatures stated since no appreciable amount of aluminum chloride has been found in the reaction zone exit gas. At the temperatures noted, the aluminum fluoride brings about a redistribution of fluorine and'the other-halogen atoms present to produce aliphatic fluorocompounds richer in fluorine than the original starting material. Operations show that the composition of the aluminum fluoride does not change, and hence it appears that the aluminum fluoride does not act as a fiuorinating agent in the usual sense and provides substantially no available fluorine during the course of the reaction. When CClsF is employed as starting material, the overall reaction involved appears to be represented by the following equations:

2CC13F- CC12F2+CC14 and to some extent 300131 co1F3+2ccn and when CHClzF is used as the starting material, the reaction appears to follow with tendency to form some CHFs. In the reactions, the presence of the NO minimizes or inhibits the formation of the three fluorine atom compounds. I

Any suitable chamber or reactor tube constructed of inert material may be employed for carrying out the reaction provided the reaction zone afforded is of sumcient length and cross-sectional area to accommodate the required amount of aluminum fluoride necessary to provide adequate gas contact area, and at the same time afford suflicient free space for passage of the gas mixture at an economical rate of flow. Externally disposed reactor tube heating means such as steam jacket or electrical heaters may .be supplied. i The following examples illustrate practice of the invention as applied to use of CC13F as start- .ing material, parts and percentages'being by weight; In these examples, the disproportionation reactorused consisted of a thirty inch section of 1" I. D. nickelfpipe containing 300 cc. of AIF; prepared by the fluorination of AlCla. This catalyst was made by procedure substantially the same as in Example B, and before use was heated in a stream of nitrogen at temperature of about 300 C. for about two hours. Prior to use the catalyst was not air treated as mentioned in Example B. The crystallite size of the catalyst averaged about 200 Angstrom units radius. The reactor was electrically jacketed for heating to reaction temperatures. Gaseous CC13F material and substantially pure NO flowed through orifice fiowmeters, and product gases were scrubbed with H2804, water and caustic, and condensed at minus 78 C., and to handle any CClFs encountered, an additional condenser maintained at liquid nitrogen temperatures was used. I

Example 1.--Pure CClaF was passed through the catalyst bed at 200 C., and infrared spectrograms of the product gases showed considerable CC1F3 to be present. A quantitative run over fifty minutes gave-the following results:

CClaF charged, 137 parts Products collected:

124 parts condensed at minus 78 C. 14 parts condensed at minus 200 C.

All the condensed products were combined and distilled atatmospheric pressure in a low temperature still withthe following results:

. CPercent OII'YPTSIOD. B. P. Parts Product of GOLF Charged 12 com 34.3 32 CClzFz 52.0 16 0013i 12.0 78 con Product ratios:

CClF =0.45 lz g =2.1 CCIgF Example 2.-Immediately upon completion of Example 1, substantially pure NO at a rate of about 5% lay-weight on the basis of the CClaF charged ;(7 liters/hour) was fed together with C(ZlsF into the reactor whichwas maintained at about 200 C. Infrared; .spectrograms showed CClFz tobe completely absent. When the system had stabilized, a quantitative run was made. 167 parts of CChF were fed over a period of one hour conjointly with about 8.4 parts of N0 gas, giving an NO concentration of about 5% by weight.

The product gases were partially condensed at 0 -C., and the resulting non-condensed gases were admixed with a slow stream of oxygen to convert NO to N02. These gases were then scrubbed with concentrated H2804 to remove N02; and with caustic to eliminate residual acidity, and with CaClz for drying, and condensed at minus 78 C. No non-condensables were observed issuing from this condenser. A total of 117 parts were collected in the 0 C. trap,.and 50 parts in the minus 78 C.

trap. Combination and distillation of the products gave the following results:

10 fluoride catalyst having crystallite size below about 500 Angstrom units radius, to disproportionate a substantial amount of said compound Percent to form a two-fiuorine-atom compound, said B. P. Parts Compound gfl gg fi fl contacting operation being carried out while in Charged the presence of NO in amount not substantially in excess of 5% by Weight of said compound but trace at least sufiicient to significantly reduce the g, quantity of three-fiuorine-atom compound which +76 44 C014 would be otherwise produced.

4. The process of contacting gaseous material Example 3.In other runs using catalysts simicomprising a compound of the group consisting lar to that of Example 1, infrared spectrograms of CClsF and CHClzF, at temperature substangave the following results: tially in the range of 75-400" (3., with aluminum Run No. 2 5 Rat e, gn. P t nt o oi ri/ G013F2/ mols/hr. 00hr ooliri 0013i 1 200 1% s00 none 0.20 3.0. 2 200 1% 300 1-2 0.00 +5. 3 300 2-2.5 300 none 1.45 1.5. 4. 300 2-2. 5 300 2. 0 0. 2 about 10. 5 i. 300 22.5 300 4.0 0.1 about 20.

Thus, comparative Examples 1 and 2 show subfluoride catalyst having cyrstallite size below stantially complete elimination of CClFa formaabout 500 Angstrom units radius, to disproportion when using a relatively large amount of NO. tionate a substantial amount of said Compound Consideration of runs 1 and 2 and of runs 3-5 of to o a w -fi l e- I said con- Example 3, point up the advantages of the intasting operation being carried out While in the vention with respect to flexibility over a substanp s o N0 in amount Substantially in the tial temperature range, flexibility of usable range of y Weight of s omp u damounts of NO, minimization of CClFi producb? P 0 OOIltactiIlg a us material tion, and formation of high CC12F/CC1F2 ratios. c r a c mp d of the group sis Further, experience shows that upon cessation of PI Q and 015C121, at perature substanfeed of NO, the characteristics and properties of 57 111 e range of 75 l00 0., with aluminum t catalyst return to normal and are not fluoride catalyst having crystallite size not subversdy aff t d with respect to use in other stantiaily greater than 200 Angstrom units processes radius, to disproportionate a substantial amount I claim; of said compound to form a two-fluorine-atom 1. The process for converting CClaF to CClzFz 4Q CPmpOundi m contacting Operation being which comprises introducing a gaseous material med out W m the Presence of NO in @mount comprising C'C13F into a reaction zone containing sukstantlelly m the range of 143% by Welght of aluminum fluoride catalyst having crystallite size said cQmpoundnot substantially greater than 200 Angstrom units U process of ctll'lg gaseous material radius, heating said material in said zone at fmmpnsmg CChF at tempemture substantlelly temperature substantially in the range of 150- the range of 75400 alumlnum for a time sufficient to convert an appre 1'1de catalyst hav ng crystalhte SIZE below about ciable amount of said cone to CC1zF2,maintain- Angiirom i to dlspmportlonate a ing in said Zone during said heating the presence substantial amount of said CClsF' to form CCliFz, Of'NO in amount substantially in the range of 50 said contacting operation being carried out while 1-5% by weight of said coin, withdrawing gasf thepresence of No 9 not j eous product from said zone, and recovering said m excess of 5% b welgh? Sam 53 from said gaseous .oroduct. pound but at least sufiicient to significantly re- 2. The process of contacting gaseous material Eig of cum Whlch would be other" comprising a fluoroderivative of methane confi tai ing t r than one fluorine atom and at 1 7.; The process of contacting gaseous material h 10 en atoms other than fluorine at comprislng CClsF at temperature substantially w W0 a g 1 7 in the range of -350 C. with aluminum fluotemperature substantially in the range of 75- a a: p

v iide catalyst having crystallite size not substan- C. with aluminum fluoride catalyst having crys w t bplow about 500 Angstrom units so tially gieater than 200 Angstrom units radius, to t disproportionate a substantial amount of said radius to disproportionate a substantlal amount CClsF to form C'Cl2F2, said contacting operation of said derivative to form a two-fluorine atom y 0 fifill'lg carried out while in the presence of NO in compound said contacting operation bein car I amount substant1ally 1n the range of 1-5% by ried out while in the piesence of NO in small 6,, Weipht of CClSF amount, based on the weight of said derivative, 0 CHARLES P NIL): ER but in amount at least suflicient to significantly n. J. i reduce t quantlty of three-fllwrme-atom References Cited in the file of this patent pound which would be otherwise produced. I l

3. The process of contacting gaseous material UNITED STATES PATENTS comprising a compound of the group consisting Number Name Date of CC13F and CHC12F, at temperature substan- 2 47 Miner et ai Aug 9 1949 tially in the range of 5 Wlth aluminum 2,478,932 Miller et a1. Aug. l6, 1%!) 

1. THE PROCESS FOR CONVERGING CCL3F TO CCL2F2 WHICH COMPRISES INTRODUCING A GASEOUS MATERIAL COMPRISING CCL3F INTO A REACTION ZONE CONTAINING ALUMINUM FLUORIDE CATALYST HAVING CRYSTALLITE SIZE NOT SUBSTANTIALLY GREATER THAN 200 ANGSTROM UNITS RADIUS, HEATING SAID MATERIAL IN SAID ZONE AT TEMPERATURE SUBSTANTIALLY IN THE RANGE OF 150350* C. FOR A TIME SUFFICIENT TO CONVERT AN APPRECIABLE AMOUNT OF SAID CCL3F TO CCL2F2, MAINTAINING IN SAID ZONE DURING SAID HEATING THE PRESENCE OF NO IN AMOUNT SUBSTANTIALLY IN THE RANGE OF 1-5% BY WEIGHT OF SAID CCL3F, WITHDRAWING GASEOUS PRODUCT FROM SAID ZONE, AND RECOVERING SAID CCL2F2 FROM SAID GASEOUS PRODUCT. 